Augmented reality as one of the fields of virtual reality is a technique that combines a virtual object with a real environment to allow a user to look like an object that exists in an original environment.
Unlike the existing virtual reality targeting only virtual space and objects, the augmented reality can add and provide additional information which is difficult to acquire through only the real world by combining virtual objects with the real world. That is, since the virtual reality technique generally allows the user to be immersed in a virtual environment, the user cannot view the real environment, while the user can view the real environment and the real environment and the virtual objects are mixed in the augmented reality technique. In other words, the virtual reality replaces the real world to be viewed to the user, but the augmented reality has a distinction in that the real world is supplemented by overlapping the virtual objects with the real world to allow the user to the supplemented real world and provides better reality to the user than the virtual reality. Due to these characteristics, unlike the existing virtual reality which can be limitatively applied to only a field such as a game, the augmented reality can be applied to various real environments, particularly, the augmented reality is widely used as a next-generation display technology suitable for a ubiquitous environment.
A quadrangular marker is generally used in the related art as the real environment for augmenting the virtual objects. This allows markers of a predetermined pattern to be detected and tracked in a black frame and can detect a plurality of markers. However, when a part of the marker is occluded, it is difficult to track the marker and the marker attracts the user's eyes by high contrast of white and black to inhibit the user's view and deteriorate user's immersion.
A method of using a real object appears in order to solve the disadvantages of the quadrangular marker. Since the method, which uses a picture or a pattern of the real object, that is, its own texture for detection and tracking instead of the quadrangular marker, uses natural features of the real object, it is excellent in tracking the object even though the object is partially occluded and provides the immersion to the user.
FIG. 1 is a flowchart of a method for tracking multiple objects using the detection of a single object in the related art.
Referring to FIG. 1, a camera image is subjected to the detection of N objects in order to detect and track N objects. That is, when object N is detected by repetitively performing a process in which object 1 is detected and thereafter, object 2 is detected with respect to an input image at time t, a list (objects 1 to N) and poses of objects detected at time t are derived. Next, a list (object 1 to N) and poses of objects detected at time t+1 are derived by repetitively performing the process of detecting objects 1 to N with respect to an input image at time t+1. Such a process is repetitively performed up to a desired time. Therefore, by such a method, the overall performance is deteriorated to 1/N as compared with the case of detecting one object per input image.
The real object tracking algorithm is optimized to a case in which only a single object exists in the camera image. According to the algorithm, whether or not the single object to be detected exists from the input image is determined and when the single object exists in the input image, a 3D pose including a 3-axis position and a 3-axis orientation of the corresponding object is estimated. Since the algorithm goes through the process, it is suitable to apply to the single object. When the algorithm is used to track multiple objects, whether or not all objects to be tracked exist for each input image should be determined. Therefore, since the processing speed is decreased in proportion to the number of objects, it is difficult to operate the algorithm in real time.